1. Field of the Invention
The invention is concerned with a wireless communication system, and in particular but not exclusively with the synchronization of values during handover.
2. Description of the Related Art
A communication system can be seen as an environment that enables communication sessions between two or more entities such as user equipment and/or other nodes associated with the communication system. The communication may include, for example, communication of voice, data, multimedia and so on. A session may, for example, be a telephone call or multi-way conference session, or a communication session between a user equipment and an application server (AS), for example a service provider server. The establishment of these sessions generally enables a user to be provided with various services.
A communication system typically operates in accordance with a given standard or specification which sets out what the various entities associated with the communication system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely, user equipment is provided with a circuit switched service and/or a packet switched service. Communication protocols and/or parameters which shall be used for the connection may also be defined. In other words, a specific set of “rules” which the communication can be based on needs to be defined to enable communication by the system.
Communication systems providing wireless communication for user equipment are known. An example of the wireless systems is the PLMN (Public Land Mobile Network). PLMNs are typically based on cellular technology. In cellular systems, a base transceiver station (BTS) or similar access entity serves wireless user equipment (UE) known also as mobile stations (MS) via a wireless interface between these entities. The communication on the wireless interface between the user equipment and the elements of the communication network can be based on an appropriate communication protocol. The operation of the base station apparatus and other apparatus required for the communication can be controlled by one or several control entities. The various control entities may be interconnected.
The field of wireless communications is evolving at a rapid pace. At present many applications are being developed for so-called third generation systems, for example UMTS (Universal Mobile Telecommunications System). System designers are also aware that most third generation systems have to be made compatible with second generation systems, for example GSM, and also with various other existing and emerging technologies, for example GPRS (General Packet Radio Service), EDGE (Enhanced Data for GSM Evolution), etc.
FIG. 1 shows a UTRAN (UMTS Terrestrial Radio Access Network) architecture having UE (User Equipment) 2 which transmits to and receives information from base stations indicated as Node B elements 4. Each Node B element 4 can have a plurality of cells, each cell being a RF coverage area provided by a transceiver. That is, each Node B element may consist of a plurality of transceivers each supplying their own cell coverage area. A plurality of Node B elements 4 are controlled by a RNC (Radio Network Controller) 6 and communicate over the so-called Iub interface. The RNC 6 is able to interface with the CN (Core Network) 8 over the so-called Iu interface. The CN 8 contains for example elements such as a MSC (Mobile Switching Center), a SGSN (Serving General packet radio services Support Node), etc.
Broadly speaking, the portion of the UTRAN architecture indicated between the two horizontal dotted lines 10 and 12 is known as the RNS (Radio Network Sub-system). More specifically, each RNS is defined as containing a single RNC element 6, which is responsible for the resources and transmission/reception in a set of cells. That is, a single RNS is defined to contain a single RNC element 6 and all the node B elements 4 that it controls. In contrast multiple RNS's require multiple RNC's.
Consider an embodiment in which a typical mobile station takes the form of one of the UE elements 2 shown in FIG. 1, it can be appreciated that the mobile subscriber is able to roam throughout the network. In such a situation it can happen that all of the RF (Radio Frequency) links to the mobile station are controlled by another RNC, different to the RNC from where the call was started. In this situation there are two possibilities:    1) Traffic can be routed to the new RNC by signaling over the IUR interface that exists between different RNC elements, and in so doing the original connection through the old RNC (i.e. where the call was started) can be maintained.    2) The original connection is completely transferred to the new RNC (e.g., where the UE 2 has roamed), and in so doing the old radio links between the relevant UE and the old RNC are released.
The first possibility is known as a so-called “anchoring” approach, whereas the second possibility is known as a so-called “SRNS” (Serving Radio Network Sub-system) relocation.
Embodiments of the invention are primarily concerned with the second possibility (i.e. SRNS relocation), and include the techniques associated with so-called “inter RNC hard handover”. An RNC is capable of assuming different roles. For example, during relocation a so-called “drift RNC” (DRNC) is present. The DRNC is not connected to the core network (i.e. has no Iu,) interface and is used to support the radio resources of the UE during handover. The DRNC can be thought of as being similar to a temporary target RNC (without a link to the core network). That is, the DRNC is capable of supporting the radio link being relocated, i.e. between the UE and the new RNC responsible for controlling the cell to be handed over to of the relevant Node B element. For SRNS relocation there are already radio links between the DRNS and the UE before relocations starts, whereas for inter RNC hard handover there are none. The present invention is concerned with both situations.
Embodiments of the present invention are particularly concerned with the situation when a “ciphering” procedure is being used over the radio link. Broadly speaking, ciphering is used to maintain the security of radio bearer connections between the UE 2 and the RNS 6. The ciphering algorithm and its relevant parameters will be explained in more detail later herein.
At present, if an SRNS relocation is to be performed it is necessary for the UE to send new ciphering parameters to the new RNC. However, this causes a relatively long break in transmission over the radio bearer channels (i.e. needed to re-initialize the security afforded by a ciphering algorithm) and/or possibly result in unwanted noise components during transmission when relocation is eventually made.
An embodiment of the invention aims to synchronize a parameter during a relocation procedure and thereby overcome the aforementioned disadvantages.